1. Field of the Invention
The present invention relates to an electronic device system and an electronic camera system to/from which a secondary battery is attached/detached. It particularly relates to an electronic device system and an electronic camera system suitable for preventing occurrence of accidents such as an explosion of a secondary battery and thereby preventing destruction of an electronic device and an electronic camera to which the secondary battery is attached, to ensure their users' safety.
2. Description of the Related Art
In recent years, a secondary battery such as a nickel-hydrogen battery, lithium-ion battery, or the like has been widely used as a battery to drive an electronic device such as an electronic camera because of its excellent economic efficiency.
Moreover, in order to extend the discharge time of the secondary battery, the realization of the higher-capacity secondary battery has been planned. Therefore, the energy storage amount per unit volume of the secondary battery has been increasing. Due to an increase in the internal temperature of the secondary battery along with overcharge, overdischarge, and so on, and an increase in the internal pressure of the secondary battery, the secondary battery may explode (See Japanese Unexamined Patent Application Publication No. 2004-96919).
To prevent such accidents as the explosion of the secondary battery, it is proposed to provide a protection circuit in the secondary battery (See Japanese Unexamined Patent Application Publication No. 2004-6524).
An example of the protection circuit of the secondary battery adopts a PTC (Positive Temperature Coefficient) thermistor in the protective circuit. For example, if an excessive current flows into the secondary battery and into the PTC thermistor, the resistance value of the PTC thermistor increases. Consequently, the current which flows into the PTC thermistor is restricted. This can inhibit overcharge and the like to the secondary battery, and accordingly prevent the explosion of the secondary battery due to an increase in the internal temperature of the secondary battery with the overcharge and an increase in the internal pressure thereof. Note that the PTC thermistor has a property that its resistance value decreases as the temperature decreases. Hence, the PTC thermistor is useful as a reusable nondestructive protective component.
Further, the internal temperature of the secondary battery is detected as a value of a current, and the detected current is allowed to flow into the PTC thermistor. As a result, when the internal temperature of the secondary battery increases and a large current flows, the resistance value of the PTC thermistor increases, thereby limiting the current flowing into the PTC thermistor. There has been proposed another technique of using this current restriction as a trigger to open an explosion preventing valve provided in the secondary battery and decrease the internal pressure thereof for the explosion prevention.
Furthermore, there has been proposed a technique of using a detachable fuel cell from a power source of the electronic device. In this case, it is important to ensure the safety of the electronic device and the fuel cell. In order to achieve this, there has been another technique of allowing the attachment of the fuel cell to the electronic device after confirming that the fuel cell attached to the power source section is a genuine part of the electronic device (See Japanese Unexamined Patent Application Publication No. 2002-280044).
In the prior arts, the protection circuit is provided in the secondary battery for prevention of the explosion of the electronic device with the secondary battery attached, so as to ensure their users' safety the explosion of the secondary battery.
However, in the world today, there are many so-called imitative batteries with no protection circuit provided.
Also, there are secondary batteries provided with the protection circuit which are not ones designed exclusively for the electronic device (hereinafter called a genuine battery) but non-genuine batteries.
If the above-described imitative batteries or non-genuine secondary batteries are attached to the electronic device such as a camera, there may cause not only the explosion of the secondary battery but also harm to a body of the electronic device and its user because it is not preventable of the increase in the internal temperature, the internal pressure and the like of the secondary battery. Accordingly, in the electronic device such as the electronic camera, it is necessary to exclude these imitative batteries and non-genuine secondary batteries with an unqualified protection circuit.